The present invention relates to the composition of a refractory gun mix for use in lining ladles, tundishes, spouts, and similar equipment for use in the movement or treatment of high temperature molten metals such as molten iron or molten steel.
Various methods have been used in the past for applying a lining of agalmatolite, zircon, alumina, or other type of refractory material to such vessels for molten metal. These methods include the use of bricks, vibration molding, casting, slinging, and stamping. Among these methods, vibration molding and casting are the most commonly used due to their efficiency, speed, and economy. However, the latter two methods have the drawbacks that they involve mixing an unshaped refractory at the site of application, building a frame for molding, and other complexities.
Whereas application of an unshaped refractory by spraying does not have these drawbacks, up to the present time, it has not been possible to extensively use spray application to form the work lining of vessels for molten metal.
When using vibration molding or casting to apply an unshaped refractory to a vessel such as a ladle, a low cement castable refractory (one containing as little alumina cement as possible) is used. This is because alumina cement has the undesirable properties that it ruptures upon quick drying and that dehydration of hydrated alumina cement causes decreased strength, decreased resistance to slag, and other forms of deterioration in an intermediate temperature range (800.degree.-1000.degree. C.).
However, when an unshaped refractory is applied by spraying with a spray gun, even in dry-type spraying in which the refractory is sent under pressure to the nozzle of a spray gun where it is sprayed as it is mixed with water, the water content of conventional sprays is high (15-20%), and the resulting sprayed deposit has an undesirably low packing density, leading to a reduced service life. The quality of the deposit is therefore inferior to that of a deposit applied by vibration molding or casting.
Thus, up to the present time, gun mixes have not been used to form the entire work lining of vessels for molten metal. Conventional spraying materials such as magnesia-type or zircon-type gun mixes have been used in the hot or cold state merely for repairing local damage in vessels originally lined by vibration molding or casting.
Thus, there is a need for a low cement castable refractory material which can be applied by spraying and which produces a deposit equal in quality to deposits applied by vibration molding or casting so that spraying can be used not only for the repair of locally damaged areas but for forming the entire work lining of the above-mentioned containers for molten metals.
Various methods have been studied of reducing the water content of gun mixes at the time of application, such as using various particle sizes and various types of binders in the gun mix. However, no satisfactory method has yet been found. For example, the mere addition of a deflocculant to deflocculate a fine powder portion having a particle diameter of at most 74 microns is ineffective, since a deflocculant requires approximately 3-5 seconds to deflocculate, whereas in dry-type spraying, less than 1 second elapses between the time the refractory powder is mixed with water in the nozzle of a spray gun and the time when the spray contacts the surface on which it is to be applied. Accordingly, there is insufficient time for the deflocculant to be effective.